The present invention relates to sensing the level in a water tank on an aircraft, such as a drinking (potable) water tank on a commercial aircraft. The circuitry and control performs a test procedure at the start of each level sensing cycle to determine whether or not ultrasonic energy is being transmitted to the tank so that the measurement can be relied upon.
The use of ultrasonic sensors for determining liquid levels in various tanks is well known, in a general sense. In the case of the potable water tanks on aircraft, the level sensing is done at repeating cycles, and it is important to determine that the ultrasonic probe and associated circuitry is operating correctly when a water level is to be determined.
The present invention relates to a built-in or automatic test procedure for an ultrasonic sensor, designed specifically for potable water tanks on aircraft. The determination of water level using ultrasonic transducers is known. A burst of ultrasonic energy is output from the transmitter, and the transmitter is shut off. The time between the sending of the ultrasonic energy and the return of an echo is used to determine the level of the liquid in the tank.
The present invention includes a sensor assembly having a switch that is actuated when an ultrasonic transducer in the sensor assembly is physically and acoustically coupled to the tank surface to initiate a transmitter circuit.
The transmitter is excited with a high energy pulse. A portion of the acoustic energy generated by the transmitter is detected by the receiver before the energy ever leaves the transducer housing. This is referred to as internal ringing. If the internal ringing is above the detect threshold for a select period of time, the transmitter is determined to be operable.
The built-in test procedure is followed each time the level sensor cycle is started and repeated. The test procedure will indicate that the transducer is providing sufficiently high levels of energy for proper level sensing. Ultrasonic coupling between the ultrasonic transducer and tank is indicated when the microswitch is actuated.
Standard circuitry is utilized for the depth measurement, and is shown in block diagram form.